Thermostat

ABSTRACT

A thermostat including a housing assembly, a snap-acting thermally responsive actuator, and a control switch is disclosed having a switch operating arrangement coacting with the switch and the actuator. The switch operating arrangement includes a lever structure hinted to the thermostat housing assembly for transmitting motion between the switch and the actuator by pivoting about the hinge. Heat transfer to the hinge is minimized so that movement of the lever is not impeded by the effects of heat on the hinge. The lever structure slidably engages the switch during movement about the hinge resulting in gradual wearing away of the switch engaging lever portion which compensates for normally occurring switch contact erosion. In one embodiment of the invention the switch operating arrangement includes a manually operated trip-free resetting mechanism which is constructed and arranged to apply a limited resetting force to the switch for preventing premature reclosing of the switch contacts and avoiding the possibility of damage to the switch.

"United States Patent [191 Semple Dec. 2, 1975 1 THERMOSTAT {75] Inventor: Alexander MacGregorSemple,

Oakville, Canada [731 Assignee: Ranco Incorporated, Columbus,

Ohio

{22] Filed: Sept. 30, 1974 [21] Appl. No.: 510,700

[52} U.S. Cl. 337/130; 337/56; 337/114; 337/342; 337/348; 337/354 [51] Int. Cl. H0111 61/00 [58] Field of Search 337/36, 46, 48, 49. 56, 337/1l4.115, 116, 117,118,130, 340, 342, 349, 351, 354

[56] References Cited UNITED STATES PATENTS 2,668.889 2/1954 Baak 337/351 X 3,405.380 10/1968 Riebs 337/36 3,573,700 4/1971 Schmitt 337/354 3,768,057 10/1973 Sekira et a1 337/354 X Primary Examiner-J. D. Miller Assistant ExaminerFred E. Bell Attorney, Agent, or FirmWatts, ll-loffmann, Fisher & Heinke Co.

[57] ABSTRACT A thermostat including a housing assembly, a snapacting thermally responsive actuator, and a control switch is disclosed having a switch operating arrangement coacting with the switch and the actuator. The switch operating arrangement includes a lever structure hinted to the thermostat housing assembly for transmitting motion between the switch and the actuator by pivoting about the hinge. Heat transfer to the hinge is minimized so that movement of the lever is not impeded by the effects of heat on the hinge. The lever structure slidably engages the switch during movement about the hinge resulting in gradual wearing away of the switch engaging lever portion which compensates for normally occurring switch contact erosion.

In one embodiment of the invention the switch operating arrangement includes a manually operated trip-free resetting mechanism which is constructed and arranged to apply a limited resetting force to the switch for preventing premature reclosing of the switch contacts and avoiding the possibility of damage to the switch.

9 Claims, 9 Drawing Figures Sheet 1 of3 Dec. 2, 1975 U.S. Patent THERMOSTAT BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to thermostats and more particularly relates to thermostats for controlling operation of electrical equipment or appliances in response to sensed temperatures either by cycling the equipment or by deactivating the equipment until the thermostat is reset.

2. Prior Art Equipment such as cloths dryers, water heaters, etc., have utilized thermostats for cycling operation of heaters to control operating temperature ranges as well as thermostats which protect the equipment by terminating operation of the heaters when excessive temperatures are sensed.

Thermostats constructed for these purposes have been of generally similar construction and included a housing assembly formed by a molded plastic housing body and electrical terminal members, a switch assembly supported by the housing assembly, and a thermally responsive actuator for operating the switch assembly.

The switches normally include a stationary contact supported by a terminal member, a moving contact, and a switch blade which supported the moving contact for motion toward and away from engagement with the fixed contact. The blade connected the moving contact to a terminal member. The switches were constructed so that the contacts were normally closed and were opened by the actuator when a predetermined temperature was sensed.

The switch actuators were normally formed by bimetal diaphragms which flexed according to the temperature of the diaphragm itself, or by diaphragms which were subjected to temperature related pressure forces of a confined fluid and flexed accordingly.

Thermostats of the nature referred to were often required to control relatively large current flows and for this reason the contacts had to be opened and closed quickly to avoid excessive contact erosion resulting from arcing and the possibility of the contacts being welded together. Accordingly, some designs utilized snapacting diaphragms for operating normally slow make and break switches, some designs employed slow moving diaphragms to operate snap switches, and still other designs employed snap-acting diaphragms to operate snap-acting switches.

Regardless of the particular design, the flexure of the diaphragm was commonly transmitted to the switch by a switch operator formed by a nonconductive, heat insulative pin extending between the diaphragm and the switch blade. The pin slidably supported by the housing assembly, usually in a closely conforming bore which guided the pin. when the diaphragm flexed in response to an increase in the sensed temperature the pin moved the switch blade to open the switch contacts. When a reduction in temperature was sensed, or when the thermostat was reset, the pin was returned to its initial position and the switch contacts were reclosed.

The operating pin and its supporting structure were generally in relatively close proximity to the switch contacts and when large currents flowed through the switch a significant amount of heat was produced causing the pin and its supporting structure to heat up. In some circumstances'the heat generated by the switch tend to cause the operating pin to seize in its support structure which in turn prevented the thermostat from operating properly.

Thermostats which cycle equipment in accordance with sensed temperatures must be constructed to cycle an extremely large number of times (e.g., several hundred thousand cycles) without excessive shifting of the preset temperature levels at which the switch is opened and closed. Snap-acting diaphragms used in such thermostats inherently exhibit a limited degree of temperature responsive slow movement (called pretravel) prior to snapping through center. After a large number of cycles and/or a long period of time the sensed temperatures at which the pretravel occurs tend to shift somewhat even though the sensed temperature level at which the diaphragm actually snaps through center may remain substantially constant.

Shifting of the temperature levels which cause the diaphragm to pretravel has, in the past, caused the effective setting of the thermostat to change, or drift, after a large number of cycles because of the combined effects of the change in temperature response of the diaphragm during pretravel and switch contact erosion.

Even when the switch contacts are snapped open and closed by a snap-acting diaphragm a perceptible amount of switch contact erosion occurs. Over thousands of switch operations the contacts can erode sufficiently that the switch is opened by the action of the diaphragm during the pretravel period of its operation. Thus the sensed temperature to which the thermostat actually responds is shifted from the preset level. The extent of the shift in the thermostat setting is not easily predictable and can be sufficiently great that thermostats will not function acceptably throughout their normally expected lifetime. Moreover, because the diaphragm pretravel occurs at a slow rate, the premature opening of the switch contacts occurs slowly tending to result in arcing and consequent damage to the contacts.

Resettable thermostats which are used to protect equipment from operating at excessive temperatures normally open an electrical power supply circuit to the equipment when excessive temperatures are detected and do not reclose the circuit until they are reset. The overall construction of resettable thermostats can be substantially the same as cycling thermostats except that the switch actuating diaphragms in resettable thermostats generally do not flex appreciably in response to reductions in sensed temperature after the switch contacts have been opened. Resetting mechanisms have been incorporated in these thermostats for reclosing the switch contacts and resetting the diaphragm. The resetting mechanisms have generally included a manually depressible reset button.

Excessive temperatures generally occcur in appliances when certain maintenance procedures are required. For example, when the lint trap in a clothes dryer is sufficiently filled that air flow through the dryer is impeded, the air temperature in the dryer becomes excessive resulting in the thermostat terminating operation of the dryer. Theoretically, the operator should clean the lint trap and then reset the thermostat to restart the dryer.

In some prior art thermostats, it was possible to reclose the thermostat switch contacts by depressing the reset button when the excessive temperature level was still being sensed. When such thermostats were employed an operator who was unfamiliar with maintaining the equipment, or who simply did not care whether the equipment was damaged, could secure the reset button in its depressed position and effectively prevent the thermostat from operating at all by maintaining the thermostat switch contacts closed at all times.

In order to prevent damage to equipment as a result of operator abuses the prior art proposed resetting mechanisms which were ineffective to reclose the thermostatic switch contacts until the sensed temperature had been reduced below the predetermined excessive level. This type of resetable thermostat has been known as trip-free.

Prior art trip-free thermostats have sometimes employed relatively complicated resetting mechanisms which increased the cost of manufacture and tended to reduce reliability. Other mechanisms have been constructed in such a way that the blade of the thermostatic switch could be yieldably bent by forces applied to it when attempts were made to reset the thermostat prematurely and excessive force was applied to the resetting mechanism.

SUMMARY The present invention provides a new and improved thermostat which is constructed and arranged so that seizing of switch operating components as a result of heat produced by the closed contacts of the thermostatic switch is avoided and shifting of preset sensed temperature levels to which the thermostat responds as a result of switch contact erosion is minimized. The invention also provides an improved trip-free resetting mechanism which is of uncomplicated reliable construction and insures against mechanical damage to the thermostat switch when attempts are made to prematurely reset the thermostat.

A thermostat constructed according to a preferred embodiment of the invention includes a housing assembly, a control switch supported by the housing assembly, a thermally responsive switch actuator attached to the housing assembly, and a switch operating arrangement for operating the switch in cooperation with the switch actuator.

The preferred housing assembly includes a molded plastic housing body defining a recess and a pair of spaced apart terminal members attached to the housing body in the recess.

The switch is disposed in the housing recess and includes a stationary contact supported by one terminal member, a movable contact, and a resiliently flexible blade supporting the movable contact and supported itself by the other terminal member. The switch blade is cantilevered to its terminal member at one end and carries the movable contact adjacent its projecting end. The switch assembly is constructed so that the blade normally urges the switch contacts into engagement to complete a circuit through the terminal members. The blade is resiliently defle'ctable to disengage the contacts.

The thermally responsive actuator is fixed to the housing assembly across the recess and includes a flexible snap-acting diaphragm which is accurately located with respect to the housing body and switch. The diaphragm can be of any suitable construction but in the preferred construction is a thin, dished metal disc which is acted upon by the pressure of a confined fluid and snapped over center in response to temperature related fluid pressures.

The switch operating arrangement comprises a switch operating unit for transmitting motion from the diaphragm to the switch. The operating unit comprises a lever structure having a lever portion engageable with the switch blade between its ends, a lever portion engageable with the diaphragm at its center, and a heat insulative lever body carrying the lever portions and extending transversely to the direction of movement of the diaphragm.

A hinge construction interconnects the lever body and the housing assembly so that the lever structure moves about the hinge axis to transmit motion between the actuator and the switch blade. The hinge is located remote from the switch contacts and is formed by pintles integral with the lever body and bearing sockets defined by the housing body. The insulative nature of the lever body material, along with the pivotal motion of the lever body and the location of the hinge remote from the switch contacts assures against the lever body seizing as a result of heating from the switch contacts.

The new thermostat is constructed and arranged so that changes in the thermostat setting due to switch contact erosion after a large number of cycles are minimized. The switch blade engaging lever portion engages the same face of the blade which supports the moving switch contact. Because of the pivotal motion of the lever, the blade engaging lever portion engages the switch blade with a distinct sliding motion along the blade whenever the contacts are opened or closed. The relative sliding of the blade contacting lever portion along the blade results in wearing away of the lever portion and this wearing of the lever portion tends to compensate for switch contact erosion which occurs during normal cycling of the thermostat. Thus, even though the diaphragm may exhibit pretravel prior to its snap movement and the sensed temperature range within which the pretravel occurs may shift after a large number of diaphargm cycles, the wearing of the lever portion compensates for the contact erosion and minimizes the risk of the switch contacts being opened by diaphragm pretravel.

In accordance with one preferred embodiment of the invention an improved trip-free resettable thermostat is provided. The switch operating arrangement includes a switch resetting mechanism which is effective to reclose the switch contacts and reset the diaphragm by snapping the diaphragm back over center. The resetting mechanism comprises a manually actuable pin supported by the housing body for limited movement toward the switch blade and a resilient force transmitting structure, preferably formed by a spring element coacting with the pin and the blade, for resiliently transmitting force from the pin to the blade for reclosing the switch contacts and resetting the diaphragm.

When the sensed temperature becomes excessive the diaphragm snaps over center to open the switch contacts. Subsequently when the sensed temperature is reduced below the excessive level the reset is depressed to reset the thermostat. In this condition of the thermostat the spring element transmits sufficient force to the diaphragm via the switch blade and lever structure to enable the diaphragm to be reset and the switch contacts reclosed.

If an attempt is made to reset the thermostat prematurely, i.e., if an excessive temperature continues to be sensed when the resetting mechanism is operated, the limited reset pin movement limits the amount of force applied by the pin to the spring element and the spring element cannot transmit sufficient force to the blade to enable the diaphragm to be reset. Accordingly, the switch contacts cannot reclose.

Because of the resiliency of the spring element and the limited travel of the resetting pin the switch blade is not subject to being bent or broken during resetting or attempted resetting of the thermostat.

Further features and advantages of the present invention will become apparent from the following detail description of preferred embodiments made with reference to the accompanying drawings which form a part of the specification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view of a thermostat embodying the present invention;

FIG. 2 is a cross-sectional view seen approximately from the plane indicated by the line 2-2, FIG. 1;

FIG. 3 is a cross-sectional view seen approximately from the plane indicated by the line 3-3, FIG. 2;

FIG. 4 is a cross-sectional view seen approximately from plane indicated by the line 4-4, FIG. 3;

FIG. 5 is a cross-sectional view seen approximately from the plane indicated by the line 5-5, FIG. 1;

FIGS. 6-8 are schematic cross-sectional views, similar to FIG. 3, showing parts of the thermostat and different operating conditions; and,

FIG. 9 is a cross-sectional view of a modified thermostat embodying the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a thermostat 10 embodying the present invention for protecting an electrically controlled appliance against damage as a result of overheating. The thermostat 10 is illustrated as mounted to a panel 12 of the appliance, which is not otherwise illustrated, by fasteners 14 and connected to electric power supply lines 16, 18 for the appliance. The thermostat 10 operates to interrupt the power supply circuit to the appliance in response to the existence of a predetermined sensed temperature level within the appliance itself. In order to re-establish the supply of power to the appliance the thermostat 10 must be manually reset.

In the preferred embodiment of the invention the thermostat 10 comprises a housing assembly 20, a thermally responsive actuator 22 which is connected to the housing assembly 20, a control switch 24 (schematically shown in FIG. 1) disposed within the housing assembly 20, and a switch operating arrangement associated with the housing assembly for effecting operation of the switch. The switch operating arrangement 25 transmits switch operating motion between the actuator 22 and the switch 24 for opening and closing the switch.

Referring now to FIGS. 2-5 the housing assembly comprises a housing body 26, terminal members 28, 30 which are fixed in the housing body 26, and insulative housing end covers 32, 34 disposed across opposite ends of the housing body. The body 26 is preferably formed from a rigid pressure molded plastic material, such as Bakelite, and defines a central transverse web 36 and generally cylindrically curved walls 38, 40 (see FIG. 3) which porject axially from the web 36 to opposite ends of the body.

The wall 38 extends concentrically about the longitudinal axis of the body and terminates at a general annular end face 42. Oppositely disposed reinforcing wall portions 38a, 38b (see FIG. 2) extend radially inwardly from the wall proper and define co-planar faces 44 recessed slightly from the face 42 for supporting the end cover 32. The wall 38 and the web 36 define a housing body recess 46 in which the switch 24 and the switch operating arrangement 25 are disposed.

The projecting end of the body wall 38 is provided with an actuator supporting structure which includes projecting locating lugs 50 spaced apart about the face 42 and peripherially spaced undercut portions 52 (FIG. 5) in the exterior surface of the wall 38 which define flange portions 54 to which the actuator 22 is connectable.

The opposite end of the body 26 defines a shallow recess 56 formed by the wall 40 and the web 36 (See FIG. 3). Spaced apart reinforcing bosses 60 extend along the wall 40 and terminate short of the end of the wall to provide end cover support faces 62 on which the end cover 34 is seated. The cover 34 is secured to the housing body by suitable screws.

The terminal members 28, 30 are rigidly fixed to the web 36 and support the switch 24 in the recess 46. The terminal members are diametrically spaced apart in the body and each is formed by a generally U-shaped electrically conductive sheet metal member securely fastened to the web.

The terminal member 27 defines a switch supporting bight portion 66 disposed with the recess 46 and legs 67 which extend from the bight portion 66 through closely conforming web slots 68 to the recess 56. One leg forms a terminal 70 which projects from the body 26 through a slot in the housing end cover 34 for connection to the power line 18. The other leg terminates within the recess 56. The bight portion of the terminal member 28 is supported by housing body ridges 72 (see FIG. 4) and the legs 67 are staked into position against the web 36 in the recess 56 so that the terminal member 28 is secured to the body.

The terminal member 30 is similar to the member 28 and comprises a switch supporting bight portion 74 in the recess 46 and legs 75 projecting through conforming web slots 76 toward the recess 56. One leg 75 forms a terminal 78 which projects from the body through the end cover 34 for connection to the line 16 while the other leg terminates in the recess 56. Each of the legs 75 have tab portions 75a disposed in the recess 46 and engaging the web 36. Each leg 75 is staked against the opposite side of the web 36 in the recess 56 so that the terminal member 30 is securely fastened to the housing body.

The control switch 24 includes a switch contact 80 (FIG. 3) supported by an electrically connected to the bight portion 74 of the terminal member 30 and oriented to face the web 36; a moving contact 82 disposed between the contact 80 and the web 36; and a resiliently flexible switch blade 84 which carries the moving contact 82. The blade 84 is preferably formed from a generally rectangular thin beryllium copper spring strip having opposite faces 84a, 84b and one end region 85 connected to the terminal member 28 by rivets 86 (see FIG. 4) so that the blade extends in cantilever fashion across the recess 46. The switch contact 82 is supported at the projecting blade end region 87 on the blade face 84a and is movable toward and away from the contact 80 by flexure of the blade. The blade 84 is preferably stressed to normally urge the contacts 80, 82 into engagement so that the switch 24 is normally in its closed condition. In the preferred embodiment of the invention a pair of parallel embossed stiffening regions 86 are provided on the blade 84 to restrict flexing of the blade to the vicinity of the end region 85.

When the contacts 80, 82 are engaged, a circuit is completedfrom the terminal 78 through the terminal member 30, the switch contacts 80, 82, the blade 84 and the terminal member 28 to the terminal 70. The circuit is interrupted when the blade 84 is flexed to separate the contacts 80, 82.

The thermally responsive actuator 22 operates to actuate the switch 24 is response to sensed temperatures via the switch operating arrangement 25. The actuator 22 may be of any suitable or conventional type and for the purposes of this description is illustrated as being fluid operated. The actuator 22 defines a hermetically sealed chamber 88 (See FIG. formed by a stamped metal housing body 90, a flexible diaphragm member 92 secured to the body 90 and a capillary tube 94 which is secured into the body 90 and extends from the body into the appliance toa location, or locations, at which it is desired to sense temperature. The chamber 88 is filled with a vaporizable fluid which vaporizes at any chamber location at which a predetermined relatively high temperature exists. The pressure in the chamber 88 varies according to the vapor pressure of the fill fluid at the highest temperature level existing along the capillary tube or at the wall of the body 90.

The body 90 is preferably a cup-like member defining a shallow generally conical base wall 98 having a central opening 99 at its apex which communicates with the tube 94, a projecting generally cylindrical side wall 100 which extends from the base wall 98 concentrically about the body wall 38 and a generally radially extending flange 102 which forms mounting ear portions 104 extending from opposite sides of the thermostat (see FIG. 1).

The diaphragm member is preferably formed by a thin circular disc of spring material which is welded to the body 90 about its periphery and centered with respect to the side wall 100. The housing assembly is nested in the body side wall 100 with the housing body lugs 50 firmly engaging the diaphragm 92 along its periphery. The side wall 100 is rigidly secured to the housing body by upsetting or staking portions of the side wall 100 into the housing body undercuts 52 so that the actuator 22 is securely clamped to the housing body via the flange portions 54.

With the actuator 22 and housing assembly assembled, the diaphragm 92 is centered on the longitudinal axis of the housing and is accurately positioned axially relative to the switch blade 84.

The diaphragm 92 is slightly dished to provide a central face 92a which is snap moved between stable positions on opposite sides of a plane extending through the periphery of the diaphragm. The central face 92a is surrounded by a generally frustoconical annular spring region 92b which enables the central face snap action. The spring section 92b functions somewhat like a belleville spring in that as sensed temperatures increase towards an excessive level, the pressure in the chamber 88 increases accordingly and the spring section 92b tends to flatten towards the plane of the periphery of the diaphragm. This gradual movement, which precedes snap movement of the central face 92a, is referred to as pretravel.

When the sensed temperature reaches a level which is by definition excessive for the appliance, the diaphragm 92 snaps through the plane of its periphery to a stable position in which the central face 92a projects toward the switch blade 84.

In the thermostat illustrated by FIGS. l-8 the spring section 92b is formed such that the diaphragm is relatively strongly urged towards its projecting over center position. Accordingly, when the pressure in the chamber 88 is reduced, due to reductions in sensed temperature, the diaphragm is not returned to its initial position because the forces applied to the diaphragm are insufficient to overcome the biasing force provided by the spring section 92b. In order to return the diaphragm to its initial position a manual resetting force must be applied to the central face 92a. The resetting force is applied to the diaphragm 92 and the switch 24 via the switch operating arrangement 25.

In the embodiment of the invention illustrated by FIGS. 1-8 the switch operating arrangement 25 includes a switch operator mechanism for transmitting motion of the diaphragm 92 to the switch blade 84 for opening the switch contacts and a trip-free resetting mechanism 112 for reclosing the switch contacts 80, 82 and for resetting the diaphragm 92 via the blade 84 and the mechanism 10.

The preferred switch operating mechanism 110 is constructed and arranged so that heat generated as a result of electric current flow through the closed switch contacts does not adversely affect operation of the operating mechanism and further, minimizes the possibility that erosion of the switch contacts resulting from normal opening and closing could result in any substantial shifts of the thermostat setting after a large number of cycles of operation. The switch operating mechanism 1 10 preferably comprises a lever structure formed by a lever body 114 disposed in the recess 46 between the actuator 22 and end cover 32 and the switch 24. The lever body 114 is pivotably movable about a hinge 1 16 for transmitting motion between the switch 24 and the diaphragm member 92. The lever body 114 is preferably constructed from a rigid heat insulative molded thermosetting plastic material and projects from a peripheral portion of the housing body remote from the switch contacts radially inwardly towards the longitudinal axis of the housing body.

The lever body 114 includes oppositely projecting lug-like lever portions 120, 122 which are respectively engageable with the diaphragm member 92 and the switch blade 84. The lever portion is located on the lever body in alignment with the center of the diaphragm 92 and projects through a central opening 32a in the end cover 32 for engagement with the diaphragm. The lever portion 122 is located further away from the hinge 116 adjacent the projecting end of the lever body and bears on the switch blade 84 between its end regions 85, 87 so that a relatively slight movement of the projecting end portion of the lever body 114 results in a substantial opening or closing movement of the switch contacts 80, 82.

The hinge ll6 is located remote from the switch contacts 80, 82 so that heat transfer to the hinge from the switch contacts is minimized and the possibility of the hinge 116 being heated and interferring with movement of the lever body 114 by seizing is obviated. The

ing bearing end portion 142. The sockets 134, 136 likewise each define a semicylindrical bearing face 144 and a frustoconical bearing face 146 which loosely conform to the bearing faces on the associated pintle. The frustoconical engaged bearing faces on the pintles and sockets tend to maintain the lever body centered between the sockets while the engaged semicylindrical bearing faces enable movement of the lever body about the hinge axis 148.

The housing end cover 124 extends between the diaphragm 92 and the lever body 114 closely adjacent the pintles 130, 132 to assure that the hinge 116 remains properly assembles during usage of the thermostat. Because of the offset locations of the lever portions 120, 122 along the lever body compressive forces applied to the lever body by the diaphragm 92 and the switch blade 84 create a slight force couple which is applied to the hinge 16 which also aids in maintaining the hinge properly assembled.

As the lever body 114 is pivoted about the hinge axis 148 during opening and closing of the switch contacts the lever portion 122 engages the blade 124 and undergoes a distinct sliding motion along the blade 84. The sliding motion of the lever portion 122 on the blade causes a slight abrasion, or wearing away, which reduces the height of the portion 122. Since the contact 82 and the lever portion 122 are disposed on the same face 84a of the switch blade 84, wearing away of the lever portion 122 tends to compensate for normally occurring erosion of the switch contacts 80, 82 caused by normal opening and closing.

As noted previously the diaphragm 92 undergoes a slight pretravel prior to actually snapping over center when an excessive temperature level is sensed. It has been found that snap-acting diaphragms of the character referred to tend, after a period of use, to undergo pretravel at sensed temperature levels which shift over a period of time. More progressively lower sensed temperatures the longer the thermostat is in service. In the absence of compensation for contact erosion it is possible to gradually open the contacts during the pretravel portion of the diaphragm movement at a sensed temperature which is less than that which is considered excessive. Premature opening of the contacts effectively changes the temperature level at which the thermostat is set to open the contacts. Furthermore, slow opening of the contacts during the diaphragm pretravel stage can result in the control cycling the apparatus on and off without the diaphragm snapping over center and result in further damage to the contacts as a result of arcing during slow opening and closing. As noted, the wearing away of the lever portion 122 as it coacts with the blade 84 tends to compensate for the normal contact erosion and accordingly a thermostat constructed according to the present invention is not subject to substantial drifts in its temperature level setting over long periods of use not is it subject to faulty operation and the consequent damage attendant the slow opening and closing of the switch contacts.

The trip-free reset mechanism 112 comprises a manually operated reset pin, or button, supported by the housing assembly 20 for movement along the longitudinal center line of the housing body 26 toward and away from the switch blade face 84b, and a resiliently deflectible spring element 162 coacting between the reset pin and the blade 84. As best illustrated by FIGS. 3 and 6-8 the pin 160 includes a body section 164 which projects from the closely conforming opening 166 in the housing end cover 34, a collar 168, and an end portion projecting from the collar 168 through the web 36 into the recess 46. The web 36 defines a central, shouldered through opening 172 for receiving the collar 168 and the end portion 170. The end cover opening 166 has a smaller diameter than the collar 168 so that the pin 160 is retained in the housing assembly by the end cover 34.

The pin body section 164 is manually depressible to move the pin 160 into the housing assembly toward the switch blade face 48b but the travel of the pin in the housing is limited so that the pin itself cannot engage the blade 84. The length of the projecting pin end portion 170 is selected so that when the pin is urged into the housing assembly the collar 168 engages the shoulder 172a of the web opening 172 to prevent further travel of the pin, and limit the amount of force which can be applied by the pin to the spring element 162.

The spring element 162 is preferably a leaf spring which is connected at one end to the terminal member 28 by the rivet 86 and extends cantlever fashion from the terminal member 28 adjacent the switch blade face 84b. The spring element is preferably formed with an upset dimple-like abutment spaced from the projecting end 182 of the spring. The abutment 180 is lightly biased by the spring element into engagement with the blade face 84b at a location 184 between the blade end region 85 and the location of contact between the blade 84 and the lever portion 122.

The projecting spring end 182 overlies and is aligned with the reset pin end portion 170 so that when the switch contacts 80, 82 are open to reset pin 160 can be depressed to the limit of its travel and engage and resiliently deflect the spring end 182.

If the highest sensed temperature in the appliance is below a level deemed excessive manual depression of the reset pin 160 to its limit of travel resiliently deflects the spring element 162 sufficiently that the spring element bears on the blade 84 with a force adequate to reset the diaphragm. The resetting force is transmitted through the blade 84, the lever portions 122, 120 and to the diaphragm 92 and overcomes the biasing force produced by the diaphragm spring section 92b so that the center face 920 of the diaphragm snaps through the plane of the diaphragm periphery away from the switch 24.

FIGS. 6 and 7 schematically illustrate the construction of the trip-free resetting mechanism and its relationships with the diaphragm 92, the lever body and the switch 24 when the switch contacts are closed and opened, respectively. FIG. 8 illustrates the trip-free resetting mechanism and associated components when an attempt is made to reset the thermostat while an excessive sensed temperature is made to reset the thermostat while an excessive sensed temperature exists in the appliance.

As illustrated by FIG. 8 the diaphragm face 92a has snapped over center and is urged towards the switch 24 by the biasing force of the spring section 92b and the fluid pressure in the chamber 88. The switch contacts 80, 82 are accordingly maintained open. The reset pin 160 is manually urged into the housing assembly to the limit of its travel resulting in the spring element 162 being resiliently deflected and engaging the-blade 84 with a limited resetting force.

The resetting force applied to the blade 84 is spaced from the location of engagement between the blade 84 and the lever portion 122 resulting in the blade 84 being resiliently deflected slightly to further open the distance between the contacts 80, 82. The limited resetting force transmitted by the spring element 162 is insufficient to overcome the internal fluid pressures acting on the diaphragm 92 and accordingly the diaphragm is not reset. Furthermore, the limited resetting force is insufficient to yieldably deflect, or bend, the blade 84. it should be note that the reset pin end portion 170 is spaced sufficiently from the blade 84 that the blade is not engaged by the spring end portion 182 when the present pin is depressed to the limit of its travel. Accordingly, the resetting force applied to the blade 84 is limited according to the characteristics of the spring element 162.

FIG. 9 illustrates another preferred embodiment of the invention in the form of a cycling thermostat 200 which does not employ a resetting mechanism. The thermostat 200 can be employed to control energization of electric base board heaters so that energization of the heaters is terminated when the sensed heater temperature exceeds a predetermined high limit. In such applications the thermostat 200 will automatically reclose the heater energization circuit when a predetermined, substantially lower temperature is detected. Thermostats like the thermostat 200 can also be used to cycle electric heater elements on and off within relatively narrow sensed temperature ranges depending on selected design characteristics of the thermal actuator.

Components of the thermostat 200 which are substantially the same as described in reference to FIGS. 1-8 are indicated by corresponding primed reference characters and for the most part are not described to avoid repetition. The thermostat 200 differs from the thermostat 10 in that the diaphragm 202 includes a central face 202a and a surrounding spring section 202b which coact to snap move through the plane of the diaphragm periphery to open the switch contacts 80', 82' when a predetermined temperature is sensed and snap moves back to the original diaphragm position to reclose the switch contacts when a lower predetermined temperature is sensed. The thermostat 200 thus enables sensed temperatures to be maintained within predetermined limits.

In order to accomplish this operation the diaphragm spring section is formed so that the biasing force it exerts in opposition to reclosing the switch contacts is overcome by the combination of the forces produced by the switch blade 84 and atmospheric air pressure acting on the diaphragm.

The lever body 114' and the hinge 116' are identical to those described above, as is the construction of the switch 24. Accordingly, heating of the hinge 116' from k the closed switch contacts is minimized, and wearing away of the lever portion 122' by sliding along the switch blade 84' during opening and closing movement compensates for switch contact erosion and minimizes drifting of the preset temperature levels to which the thermostat 200 responds over a large number of cycles.

While two preferred embodiments of the invention are illustrated and described in considerable detail, the invention is not to be considered limited to the precise constructions disclosed. Various adaptations, modifications and uses of the invention may occur to those skilled in the art to which the invention relates and it is the intention to cover hereby all such adaptations, modifications and uses which fall within the scope or spirit of the appended claims.

What is claimed is:

1. A thermostat comprising:

a. a housing assembly;

b. switch means disposed in said housing and comprising a firstcontact supported by said housing assembly, a second contact, snd switch blade means having a first end region supported by said housing assembly and a second projecting end region supporting said second'contact for movement into and away from engagement with said first switch contact;

c. thermally responsive actuator means connected to said housing assembly and including a surface movable relative to said housing assembly toward and away from said switch blade means in response to sensed changes in temperature, said surface movable in a direction transverse to the extent of said blade means;

d. a switch operating arrangement comprising a switch operator lever structure disposed between said thermally responsive means and said .blade means for transmitting motion of said surface of said thermally responsive means to said blade means, said lever structure having a first lever portion for engaging said surface of said thermally responsive means, a second lever portion for engaging said blade means between said first and second end regions, and a heat insulative lever body rigidly interconnecting said first and second lever portions and extending from said lever portions generally transversely of the direction of movement of said surface; and,

. hinge means interconnecting said lever body and said housing assembly for constraining movement of said first and second lever portions about a hinge axis disposed in a plane which is transverse to the I direction of movement of said surface, said hinge means located remote from said first and second contacts.

2. The thermostat claimed in claim 1 wherein said switch blade means comprises a thin resiliently deflectable switch blade member defining a blade'faee on which said second contact is supported, and said lever portion engaging said blade face for resiliently deflecting said blade member to open and close said contacts while pivoting about saidhinge axis, said second lever portion being slidable relative to. said blade face as said blade member is deflected and constructed of a material which is worn away by sliding movement on said blade member. v

3. The thermostat claimed in claim 1 wherein said thermally responsive actuator means is effective to open said contacts at a predetermined sensed temperature level and maintain said contacts open thereafter regardless of the sensed temperature level, and said switch operating arrangement further comprises a tripfree resetting mechanism for reclosing said contacts and resetting said actuator for further operation, said resetting mechanism comprising a pin member supported by said housing assembly for limited movement toward said switch blade means and said surface of said thermally responsive means and resiliently deflectable means coacting between said pin member and said switch blade means for transmitting limited resetting force from said pin to said blade means.

4. A resettable thermostat comprising:

a. a housing assembly;

b. thermally responsive means attached to said housing assembly comprising a snap moving member having a surface portion which snap moves transversely to the extent of said snap moving member relative to said housing assembly from a first position to a second position in response to a predetermined sensed temperature level;

. switch means comprising a first contact supported by said housing assembly, a second contact, and a resiliently deflectable blade carrying said second contact at a first blade end region and fixed to said housing assembly at a second blade end region, said blade normally biasing said second contact into engagement with said first contact;

d. a switch operating arrangement comprising:

i. switch operator means disposed between said snap moving member and said blade for transmitting motion of said surface portion of said snap moving member to said blade as said surface portion moves from said first position to said second position, said operator means effective to resiliently deflect said blade and open said contacts and including an operator portion engaging a first face of said blade at a location between said blade end regions; and,

resetting means for reclosing said switch contacts and resetting said surface of said snap moving member from said second position to said first position;

iii. said resetting means comprising a pin member supported by said housing assembly for movement toward a second face of said blade opposite to said first face, structure limiting movement of said pin member toward said blade, and resiliently deflectable force transmitting means between said pin member and said blade for applying a limited resetting force to said blade.

5. A resettable thermostat as claimed in claim 4 wherein said resiliently deflectable force transmitting means comprises a spring element engaged with said blade and having a deflectable portion engageable by 14 said pin member, said spring element engaged with said blade at a location between said blade end regions and spaced from the line of motion of said pin member.

6. A resettable thermostat as claimed in claim 5 wherein said structure limiting movement of said pin member comprises an abutment on said pin member and an abutment defined by said housing assembly, said abutment engageable to limit movement of said pin toward said blade with said pin spaced from said blade.

7. A resettable thermostat as claimed in claim 4 wherein said snap moving member is moved to said second position in response to said predetermined sensed temperature level and remains in said second position regardless of the sensed temperature level until reset, said resiliently deflectable force transmitting means comprising a leaf spring member effective to transmit resetting force from said pin to said snap moving member via said blade and said switch operator means, said leaf spring member deflected by said pin and effective to move said snap-acting member from said second position to said first position only when the sensed temperature level is lower than said predetermined level.

8. A thermostat comprising:

a. a housing assembly;

b. switch means supported by said housing assembly comprising a substantially fixed contact, a movable contact, and a resiliently deflectable blade supporting said movable contact along one face thereof for movement into and away from engagement with said fixed contact;

. thermally responsive actuator means for effecting operation of said switch means comprising an acutator member having a portion abruptly movable relative to said switch blade for effecting operation of said switch in response to sensed temperature; and,

d. switch operator structure between said actuator means and said blade, said operator structure comprising a blade engaging portion engageable with said blade on said one face and an operator member supporting said blade engaging portion for pivotal motion relative to said blade while transmitting motion from said actuator means to said blade with said blade engaging portion sliding along said blade during said pivotal motion and wearing away slightly during the sliding motion.

9. The thermostat claimed in claim 8 wherein said operator member is defined by a lever body and further including hinge means interconnecting said lever body and said housing assembly.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3 ,924 ,213

DATED December 2, 1975 INV ENTOR(S) I Alexander MacGregor Semple It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Abstract, line 6, "hinted" should be -hinged-; Column 1, line 12, "cloths" should be clothes--;

Column 1, line 24, "include" should be included; Column 1, line 56 "when" should be -When-;

Column 1, line 68 "tend" should be tended;

Column 6, line 56, "an should be -and-;

Column 7, line 41, after "member" insert 92;

Column 9, line 25, "16" should be ll6-;

Column 10, lines 64 and 65 delete "is made to reset the thermostat while an excessive sensed temperature";

Claim 1, paragraph b, line 3 "snd" should be -and; Claim 2, line 4, delete "and";

Claim 2, line 4, before "lever" insert second; Claim 6, line 5, "abutment" should be -abutments-.

Signed and Scaled this [SEAL] I sixth Day of Aprz'l1976 Attest:

RUTH C. MASON Arresting Officer C. MARSHALL DANN Commissioner ufPalents and Trademarks 

1. A thermostat comprising: a. a housing assembly; b. switch means disposed in said housing and comprising a first contact supported by said housing assembly, a second conTact, snd switch blade means having a first end region supported by said housing assembly and a second projecting end region supporting said second contact for movement into and away from engagement with said first switch contact; c. thermally responsive actuator means connected to said housing assembly and including a surface movable relative to said housing assembly toward and away from said switch blade means in response to sensed changes in temperature, said surface movable in a direction transverse to the extent of said blade means; d. a switch operating arrangement comprising a switch operator lever structure disposed between said thermally responsive means and said blade means for transmitting motion of said surface of said thermally responsive means to said blade means, said lever structure having a first lever portion for engaging said surface of said thermally responsive means, a second lever portion for engaging said blade means between said first and second end regions, and a heat insulative lever body rigidly interconnecting said first and second lever portions and extending from said lever portions generally transversely of the direction of movement of said surface; and, e. hinge means interconnecting said lever body and said housing assembly for constraining movement of said first and second lever portions about a hinge axis disposed in a plane which is transverse to the direction of movement of said surface, said hinge means located remote from said first and second contacts.
 2. The thermostat claimed in claim 1 wherein said switch blade means comprises a thin resiliently deflectable switch blade member defining a blade face on which said second contact is supported, and said lever portion engaging said blade face for resiliently deflecting said blade member to open and close said contacts while pivoting about said hinge axis, said second lever portion being slidable relative to said blade face as said blade member is deflected and constructed of a material which is worn away by sliding movement on said blade member.
 3. The thermostat claimed in claim 1 wherein said thermally responsive actuator means is effective to open said contacts at a predetermined sensed temperature level and maintain said contacts open thereafter regardless of the sensed temperature level, and said switch operating arrangement further comprises a trip-free resetting mechanism for reclosing said contacts and resetting said actuator for further operation, said resetting mechanism comprising a pin member supported by said housing assembly for limited movement toward said switch blade means and said surface of said thermally responsive means and resiliently deflectable means coacting between said pin member and said switch blade means for transmitting limited resetting force from said pin to said blade means.
 4. A resettable thermostat comprising: a. a housing assembly; b. thermally responsive means attached to said housing assembly comprising a snap moving member having a surface portion which snap moves transversely to the extent of said snap moving member relative to said housing assembly from a first position to a second position in response to a predetermined sensed temperature level; c. switch means comprising a first contact supported by said housing assembly, a second contact, and a resiliently deflectable blade carrying said second contact at a first blade end region and fixed to said housing assembly at a second blade end region, said blade normally biasing said second contact into engagement with said first contact; d. a switch operating arrangement comprising: i. switch operator means disposed between said snap moving member and said blade for transmitting motion of said surface portion of said snap moving member to said blade as said surface portion moves from said first position to said second position, said operator means effective to resiliently deflect said blade and open said contacts and including an operator portion engaging a First face of said blade at a location between said blade end regions; and, ii. resetting means for reclosing said switch contacts and resetting said surface of said snap moving member from said second position to said first position; iii. said resetting means comprising a pin member supported by said housing assembly for movement toward a second face of said blade opposite to said first face, structure limiting movement of said pin member toward said blade, and resiliently deflectable force transmitting means between said pin member and said blade for applying a limited resetting force to said blade.
 5. A resettable thermostat as claimed in claim 4 wherein said resiliently deflectable force transmitting means comprises a spring element engaged with said blade and having a deflectable portion engageable by said pin member, said spring element engaged with said blade at a location between said blade end regions and spaced from the line of motion of said pin member.
 6. A resettable thermostat as claimed in claim 5 wherein said structure limiting movement of said pin member comprises an abutment on said pin member and an abutment defined by said housing assembly, said abutment engageable to limit movement of said pin toward said blade with said pin spaced from said blade.
 7. A resettable thermostat as claimed in claim 4 wherein said snap moving member is moved to said second position in response to said predetermined sensed temperature level and remains in said second position regardless of the sensed temperature level until reset, said resiliently deflectable force transmitting means comprising a leaf spring member effective to transmit resetting force from said pin to said snap moving member via said blade and said switch operator means, said leaf spring member deflected by said pin and effective to move said snap-acting member from said second position to said first position only when the sensed temperature level is lower than said predetermined level.
 8. A thermostat comprising: a. a housing assembly; b. switch means supported by said housing assembly comprising a substantially fixed contact, a movable contact, and a resiliently deflectable blade supporting said movable contact along one face thereof for movement into and away from engagement with said fixed contact; c. thermally responsive actuator means for effecting operation of said switch means comprising an acutator member having a portion abruptly movable relative to said switch blade for effecting operation of said switch in response to sensed temperature; and, d. switch operator structure between said actuator means and said blade, said operator structure comprising a blade engaging portion engageable with said blade on said one face and an operator member supporting said blade engaging portion for pivotal motion relative to said blade while transmitting motion from said actuator means to said blade with said blade engaging portion sliding along said blade during said pivotal motion and wearing away slightly during the sliding motion.
 9. The thermostat claimed in claim 8 wherein said operator member is defined by a lever body and further including hinge means interconnecting said lever body and said housing assembly. 